Refrigeration system and system for separating oil from compressed gas



Nov. 5, 1968 SQUMERAI ET AL 3,408,828

REFRIGERATION SYSTEM AND SYSTEM FOR SEPARATING OIL FROM COMPRESSED GASFiled Sept. 8. 1967 INYENTORS Henri Soumeroi Harold W. Moody, Jr.

Clark B .Homilton James R. Blofl Char/s, ATTORNEYS 3,408,828REFRIGERATION SYSTEM AND SYSTEM FOR SEPARATING OIL FROM COMPRESSED GASHenri Soumerai, West Hartford, Harold W. Moody, Jr., Farmington, ClarkB. Hamilton, Wethersfield, and

James R. Blatt, Coventry, Conn., assignors to Dunham- Bush, Inc., WestHartford, Conn., a corporation of Connecticut Continuation-impart ofapplication Ser. No. 612,222, Jan. 27, 1967. This application Sept. 8,1967, Ser. No. 666,372

Claims. (Cl. 62470) ABSTRACT OF THE DISCLOSURE A refrigeration system isdisclosed having a compressor of the screw type, and a stream ofcompressed gas and oil mist is used to cool the compressor and themotor. The oil is separated by passing the stream of refrigerant gas andoil through a unit which subjects the oil-laden gas to a thoroughoil-separating treatment without restricting the flow of the oil-freegas.

This application is a continuation-in-part of application Ser. No.612,222, filed J an. 27, 1967, and covering the refrigeration system ofthe illustrative embodiment of the present invention. The presentinvention is directed to the details of structure and mode of operationinvolved in the separation of the oil which is entrained in the streamof compressed refrigerant gas.

This invention relates to refrigeration, and more in particular to arefrigeration system and method wherein the compressor is of the screwtype and the stream of compressed gas and oil passes through a specialoil separator.

An object of this invention is to provide an improved refrigerationsystem of the type having a compressor from which a stream of compressedrefrigerant gas contains oil which must be separated from the gas,Another object is to provide an improved method and means for separatingoil from compressed gas. A further object is to provide for the abovewith compressors of the screw type. Another object is to provide meansfor maintaining desirable operating conditions in a screw compressorunder varying loads and extreme conditions of use. A further object isto provide for the above in a manner which avoids the difficulties whichhave been encountered in the past with similar constructions. These andother objects will be in part obvious and in part pointed out below.

In the drawings:

FIGURE 1 is a schematic representation of one embodiment of theinvention;

FIGURE 2 is a fragmentary perspective view of the oil separator unit ofFIGURE 1, with parts broken away; and,

FIGURE 3 is an enlarged view of the wire mesh which is in the oilseparator unit of FIGURE 1.

Referring to FIGURE 1 of the drawings, a refrigeration system 2includes: a screw compressor 4 having an unloader 5 and driven by anelectric motor 6; an oil separator 8; a refrigerant discharge line 10; awater-cooled condenser 12; a liquid refrigerant line 14 extending to arefrigerant control and restrictor assembly 112 from which therefrigerant flow-s to an evaporator 26; and, a gas refrigerant returnline 32 through which the gas refrigerant returns to compressor 4.

The system also includes an oil circulating system including thefollowing in series: an oil sump 34; an oil pump 36 driven by anelectric motor 37; an oil cooler 38 through which water flows from awater inlet 40 to a water outlet 42 and which cools the oil flowing fromthe pump and, an oil filter 44. An oil supply line 46 delivers oil undercontrolled pressure through distributor lines 48 to the motor bearings50 and through lines 52 and 54 and 56 to compressor 4. Oil is alsodelivered from line 46 through a line 58 to the'unloader 5, and througha line 59 to a load control unit 60.

During operation, the dense high-pressure oil-gas mixture is dischargedfrom compressor 4 into a chamber 62 and thence through the motor whereit is discharged axially against a baffle 64. This" gas-oil mixtureuniformly blankets and cools the stator and rotor of the motor, and themotor also serves as a first-stage oil separator and removes, bycentrifugal action, the bulk of "the oil entrained in the gas. It hasbeen found that something of the order of 95% of the oilis removed bythe motor, and the oil accumulates at 66 in the bottom of the housingfrom which it flows through a line 35 to oil sump 34. The remaining fineoil mist is then separated from the gas by the action of baffle 64 andoil separator S.

The disk-like baflle 64 deflects the stream of gas radially outwardlytoward the outer wall and the oil then flows axially past the edge ofthe baflie through an annular passageway 68. Positioned in axialalignment with passageway 68 is an annular separator unit 70 whicheffectively removes the oil from the gas passing through it. Separatorunit 70 includes (see also FIGURE 2) a loosely-formed ring or annularseparator 71 of knitted wire mesh which is wound upon a perforatedtubular mandril 72. Mandril 72 forms a central gas discharge passageway74 through which the gas flows to a gas discharge tube 73, and thencepast a check valve 75 to line 10.

Separator 71 is in the form of two rolls 77 and 79, each of which isformed by a two-ply strip 81 (see FIGURE 3) of knitted wire mesh. Roll79 is twice the axial dimension of roll 77, and is formed by two strips81 side-by-side. In this embodiment strip 81 is illustratively 7 incheswide and is formed by first knitting a wire-mesh tube having 60 openingsper square inch and using steel of .011 inch in diameter. The mesh tubeis then flattened to form the twoply strip 81, and it is crimpeddiagonally of the strip to form ridges, with the crimping being A inchdeep, and with the ridges being inch wide from ridge to ridge. A strip81 is wound loosely on mandril 72 to form roll 77, and two strips 81 arewound loosely side-by-side to form roll 79. A perforated support plateis assembled on mandril-72 at the side of roll 77. The radius of roll 77is less than that of roll 79, so that there is an annular passageway 83between roll 77 and shell 61. Ilustratively, the radius of the innersurface of shell 61 is of the order of 10 inches, and the radius of roll77 is 8 /2 inches. Therefore, a portion of the annular stream of gaswith entrained oil flowing axially from passageway 68 may continue itsaxial flow through the perforations in plate 85 and along passageway 83.

The portion of the stream adjacent the periphery of baflie 64 impingesagainst plate 85 at the periphery of roll 77, and may pass through theperforations in the plate and into the roll. However, support plate 85is spaced axially from 'baflie 64, so as to provide a radial passageway76 through which the gas may flow radially inwardly to passageway 74,without passing through separator 71. Therefore, it might be expectedthat some of the gas with entrained oil will pass radially inwardlythrough passageway 76 and enter passageway 74 without giving up its oil.However, it has been found that with the arrangement herein disclosed,there is a tendency for twophase fluid flow axially through passageway76 with gas having the oil mist therein flowing along the casing walland through the perforations in plate 85 and along passageway 83, whileoil-free gas flows adjacent baflie 64 and thence radially inwardlythrough passageway 76. The oilladen gas in passageway 83 impingesagainst the rolls 77 Patented Nov. 5, 1968 .3 and 79, and there is avery substantial increase in the crosssectional area of the flow pathwhich causes a substantial reduction in the rate of flow. Hence, frompassageway 83 the gas flows or migrates radially inwardly at a very slowflow rate toward the central mandril 72. Mandril 72 and plate 85 aresheet metal of sufficient rigidity to provide the desired support, andyet the perforations are of suflicient size and number to permit therelatively free flow of the gas through the plate and through themandril wall. Hence, at the outer periphery of roll 77, some of the gaspasses through plate 85 directly into roll 77.

During the flow through rolls 77 and 79, the oil adheres to the exposedsurfaces of the wire mesh and flows downwardly and collects at thebottom of the casing 61 in the body of oil 66. There may be a tendencyfor the oil to bridge some of the passageways or perforations betweenthe adjacent portions of the wire mesh in rolls 77 and 79. Such bridgingof the passageways could be expected to cause the oil to be re-entrainedin the gas so as to reduce the effectiveness of the oil separator.However, such re-entrainrnent does not occur, apparently because of thereduced velocity of the gas flow through the wire mesh. It has beenfound that the arrangement of the illustrative embodiment is eifectiveto separate substantially all of the oil from the refrigerant gasthroughout the entire range of loading from minimum to full load. Atlight loads there is a tendency for a high percentage of the refrigerantgas to flow through rolls 7'7 and 79, whereas at increased loads thetendency toward the two-phase fluid flow causes an increased amount ofthe refrigerant gas to be free of oil and to pass radially inwardlythrough passageway 68 without passing through rolls 77 and 79.

Certain details of the construction of the illustrative embodiment areset forth above, and it has been explained that very satisfactoryresults are obtained within the full range of variations in load on thecompressor, In general the winding tension on the wire mesh must not behigh enough to prevent the free flow of the refrigerant gas at a slowrate toward the central passageway 74 formed by mandril 72. In theillustrative embodiment mandril 72 has a diameter of the order of 7inches, and battle 64 has a diameter of 14 inches and is spaced 1%inches fromplate 85. The wire mesh forming rolls 77 and 79 is ofsubstantially uniform density of the order of 15.5 pounds per cubicfoot. It must be understood that these specific dimensions and otherphysical characteristics are illustrative.

As indicated above, unloader controls the operation of the compressor sothat it compresses the amount of refrigerant required for'the load atall times. Accordingly, compressor 4 has a capacity control slide valve120 which is shown in the full-load position wherein it forms a portionof the compressor-rotor casing 122. Slide valve 120 is mounted to slideto the left from the position shown to thereby expose an opening in thebottom of the rotor casing through which the suction gas can pass backfrom the central portion of the compressor to the suction inlet. In thisway the amount of gas pumped is reduced.

Sliding valve 120 is connected through an operated spindle 124 to apiston 126 which is slidable in a cylinder 128. Piston 126 is moved tothe left from the position shown by supplying oil at a controlledpressure to the chamber 130 in the cylinder at the right of the piston.Cylinder 128 is open at its left-hand end to the suction pressure of thecompressor. Hence, when oil is supplied to chamber 130 at a pressuregreater than the discharge pressure, piston 126 is moved to the left;and, when the pressure of the oil in chamber 130 is less than thedischarge pressure, piston 126 moves to the right. Oil supply line 58 isconnected to chamber 130 through a shutoff valve 132 and a line 134.Hence, when valve 132 is open the oil at the full pressure in lines 46and 58 is supplied at once to chamber 130. Also, a flow circuit isprovided in parallel with valve 132 by line 59 and a restrictor valve136 and a shut-off valve 138 Hence, when valve 132 is closed and valve138 is opened, the oil at the pressure of line 46 flows through line 59restrictor 136, valve 138 and line 134 to chamber 130. However,restrictor 136 limits the rate of flow so that piston 126 is moved at areduced but controlled rate, whereas when valve 132 is open the pistonmoves at a rapid rate. This permits unloading rapidly by opening valve132, orunloading at a slower rate by opening valve 138.

An additional control circut is provided by a shut-off valve 140 and arestrictor 142 in aline 144 which extends between the suction inlet ofthe compressor housing and chamber 130. Hence, when valve 140 is openthe oil in chamber 130 is free to flow through line 134, restrictor 142,line 144, and valve 140 to the compressor casing. As indicated above,when the compressor is operating, the pressure of the compressed gas atthe discharge side of the compressor urges sliding valve toward itsfull-load position. Hence, when valve 140 is open, the pressureequalizes on the two sides of the piston because of the flow of oil fromchamber 130, and the discharge pressure acting on slide valve 120 movesthe slide and piston 126 back to the position shown. Restn'ctor 142controls the rate of flow of oil from chamber and therefore controls therate of movement of the piston from a partialload position to thefull-load position.

The oil pressure in line 46 is controlled by a control unit 146 whichhas a valve 148 in a line 150 extending from line 46 to sump 34. Acontrol line 152 extends from unit 146 to the discharge chamber 62 ofthe compressor so that unit 146 is responsive to the compressordischarge pressure. Unit 146 and its valve 148 act as a relief valve tomaintain a pressure in line 46 which is a predetermined amount above thepressure in chamber 62. Illustratively, when the compressed gas pressurein chamber 62 is 200 pounds per square inch, the pressure in line 46 is240 pounds per square inch. Hence, the oil delivered to the compressorthrough the various lines 48, 52, 54 and 56, and through lines 58 and 59to the unloader is maintained at a predetermined value above thecompressor discharge pressure. This insures a proper and adequate supplyof oil to the motor bearings and to the compressor. It also insures thatthe unloader will operate properly. The opening of valve 132 when thecompressor is partially or fully loaded will unload it at a rapid rate.The opening of valve when the compressor is partially or completelyunloaded will fully load it at a controlled rate.

It has been pointed out above that the heavy mixture of compressed gasand oil mist provides a very satisfactory cooling of the motor. The oilmist produces a scrubbing action which improves the heat exchange factorand increases the cooling of the motor. The oil which is sup plied tothe compressor may contain some refrigerant and that refrigerant tendsto flash and to aid in the cooling effect of the oil. It is thus seenthat the refrigerant and the oil are circulated through separate cycles,but that inter-relationship is maintained which provides an improvedmode of operation. Pump 36 is started prior to the starting of motor 6so that the oil pressure builds up and provides oil for the motor andcompressor, and the desired oil pressure is provided for the unloader.The controls also provide automatic unloading at start-up.

The system of FIGURE 1 includes standard components and controls. It isalso understood that the embodiment herein disclosed is illustrative,and it is contemplated that changes and modifications may be made withinthe scope of the invention. Reference may be had to the above-identifiedco-pending application, which is incorporated herein by reference.

What is claimed is:

1. In a refrigeration system of the type having a motorcompressor of thetype wherein a stream of compressed refrigerant gas containing asubstantial amount of oil is delivered for passage to a refrigerantcondenser, an oil separator to separate the oil from the refrigerant.gas comprising, means including an enclosure wall forming a flow path ina general direction which is along and parallel to an oil-separatingaxis, baflle means extending transversely of said axis positioned todivert the stream of gas radially outwardly from said axis and formingwith said enclosure wall an axial passageway path parallel to said axis,a body of mesh positioned along said flow path upon the downstream sideof said baffie means and spaced axially downstream and thereby providinga free passageway extending radially inwardly from said axialpassageway.

2. Apparatus as described in claim 1 wherein said enclosure wall is asubstantially cylindrical wall having its axis substantially parallel tothe axis of the motor and which includes a perforated mandril forming anaxial gas discharge passageway, and wherein said body of mesh is anannular body of knitted wire surrounding said mandril.

3. Apparatus as described in claim 2 wherein said knitted mesh is formedof steel wire which has been strip and the strip has been wound into aspiral.

4. Apparatus as described in claim 2 wherein said knitted mesh is formedby spiral layers of knitted mesh and the density in terms of weight ofmetal per cubic foot is of the order of 15.5 pounds.

5. Apparatus as described in claim 1 wherein said enclosure wallpresents a substantially cylindrical inner surface and said bafiie meansis centrally positioned with respect to said inner surface and ispositioned to make said axial passageway annular, and wherein said bodyof mesh is an annular body of wire mesh, and a perforated gas dischargeconduit positioned within said annular body, said annular body being ofsuch density as to permit the flow of refrigerant gas therethrough at arate which is insufficient to cause re-entrainment of oil which isseparated from the gas.

References Cited UNITED STATES PATENTS 2,610,480 9/1952 Briscoe 62-493LLOYD L. KING, Primary Examiner.

